Characterization of bronchoalveolar lymphocytes during a specific antibody-forming cell response in the lungs of mice

The goal of this study was to characterize the total numbers and phenotypes of lymphocyte subpopulations recovered by bronchoalveolar lavage during an experimental immune response in the lung parenchyma. Inbred mice (C57BL/6) were primed systemically and then challenged intratracheally with sheep red blood cells, a T-cell-dependent antigen. At various days later, we performed differential cell counts, measured the concentrations of specific antibody-forming cells, and determined lymphocyte phenotypes in bronchoalveolar lavage fluid by flow cytometry, distinguishing lymphocytes by light scatter parameters. We found that the numbers of lymphocytes recovered by bronchoalveolar lavage increased significantly in primed mice challenged with the priming antigen but not in three control groups: unprimed mice challenged intratracheally with the same dose of sheep red blood cells, primed mice challenged with hydrochloric acid, and primed mice challenged with a non-cross-reacting erythrocyte. At all times tested the concentrations of antibody-forming cells in bronchoalveolar lavages were identical to those of cells from minced lungs. Helper T-cells (L3T4-positive) increased earliest and constituted the majority of lymphocytes in bronchoalveolar lavage fluid throughout the immune response. We conclude: first, that there is a major influx of lymphocytes into the lungs during the development of a specific pulmonary immune response; second, that this lymphocyte influx occurs only in the presence of an antigen-driven response; third, that lymphocytes specific for the challenging antigen are in equilibrium between the bronchoalveolar and interstitial compartments; fourth, flow cytometry can be used to determine surface phenotypes of bronchoalveolar lymphocytes in mice.